1. Field of the Invention
This invention relates to a device useful during orthodontic treatment for correcting the position of one dental arch relative to the other. More specifically, this invention relates to a force module device for urging the lower dental arch either in a forwardly or a rearwardly direction relative to the upper dental arch in order to improve occlusion.
2. Description of the Related Art
Orthodontic treatment involves movement of malpositioned teeth to orthodontically correct positions. During treatment, tiny orthodontic appliances known as brackets are often connected to anterior, cuspid and bicuspid teeth, and an archwire is placed in a slot of each bracket. The archwire forms a track to guide movement of the brackets and the associated teeth to desired positions for correct occlusion. Typically, the ends of the archwire are held by appliances known as buccal tubes that are secured to the patient's molar teeth. The brackets, archwires and buccal tubes are commonly referred to as "braces".
The orthodontic treatment of some patients include correction of the alignment of the upper dental arch with the lower dental arch. For example, certain patients have a condition referred to as a Class II malocclusion where the lower dental arch is located an excessive distance in a rearwardly direction relative to the location of the upper dental arch when the jaws are closed. Other patients may have an opposite condition referred to as a Class III malocclusion wherein the lower dental arch is located in a forwardly direction of its desired location relative to the position of the upper dental arch when the jaws are closed.
Orthodontic treatment of Class II and Class III malocclusions are commonly corrected by movement of the upper dental arch as a single unit relative to movement of the lower dental arch as a single unit. To this end, forces are often applied to each dental arch as a unit by applying force to the brackets or buccal tubes, the archwires, or attachments connected to the brackets, buccal tubes, or archwires. In this manner, a Class II or Class III malocclusion can be corrected at the same time that the archwires and the brackets are used to move individual teeth to desired positions relative to each other.
Correction of Class II and Class III malocclusions is sometimes carried out by use of a force-applying system known as headgear that includes strapping which extends around the rear of the patient's head. The strapping is often connected by tension springs that, in turn, are connected to the buccal tubes, the brackets or one of the archwires. Additionally, as an alternative for correction of Class III malocclusions, the strapping may be connected by tension springs to a chin cup that externally engages the patient's chin. In either instance, the strapping and springs serve to apply a rearwardly-directed force to the associated jaw.
However, headgear is often considered unsatisfactory because it is visibly apparent. Headgear may serve as a source of embarrassment, particularly among child and teenage patients who may experience teasing from classmates. The embarrassment can be somewhat reduced if the orthodontist instructs the patient to wear the headgear only at night, but unfortunately such practice may lengthen treatment time since the desired corrective forces are applied during only a portion of each calendar day.
Consequently, many practitioners and patients favor the use of intra-oral devices for correcting Class II and Class III malocclusions. Such devices are often located near the cuspid, bicuspid and molar teeth and away from the patient's anterior teeth. As a result, intra-oral devices for correcting Class II and Class III malocclusions are hidden in substantial part once installed and eliminate much of the patient embarrassment that is often associated with headgear.
Orthodontic force modules made of an elastomeric material have been used in the past to treat Class II and Class III malocclusions by connecting a pair of such force modules between the dental arches on opposite sides of the oral cavity. Elastomeric force modules are often used in tension to pull the jaws together in a direction along references lines that extend between the points of attachment of each force module. Such force modules may be an O-ring or a chain-type module made of a number of integrally connected O-rings. However, these modules are typically removable by the patient for replacement when necessary, since the module may break or the elastomeric material may degrade during use to such an extent that the amount of tension exerted is not sufficient.
Unfortunately, orthodontic devices such as headgear and removable force modules are not entirely satisfactory for use with some patients, because the effectiveness of the devices is dependent upon the patient's cooperation. Neglect of the patient to faithfully wear the headgear each day or install new elastomeric force modules as appropriate can seriously retard the progress of treatment and defeat timely achievement of the goals of an otherwise well-planned treatment program, resulting in an additional expenditure of time for both the patient and the orthodontist.
As a result, a number of intra-oral devices that are non-removable by the patient have been proposed in the past to overcome the problems of patient cooperation associated with headgear and with removable intra-oral force modules. For example, U.S. Pat. Nos. 4,708,646, 5,352,116, 5,435,721 and 5,651,672 describe intra-oral devices with flexible members that are connected to upper and lower dental arches of a patient. The length of the members is selected such that the member is curved in an arc when the patient's jaws are closed. The members have an inherent bias that tends to urge the members toward a normally straight orientation to provide a force that pushes one dental arch forwardly or rearwardly relative to the other dental arch when the jaws are closed.
U.S. Pat. Nos. 5,645,424 and 5,678,990 describe intra-oral devices for correcting Class II and Class III malocclusions having linkage that includes pivotal connections. The devices in both of these references have a somewhat overall "Z" shaped configuration. A device having a somewhat similar overall configuration is shown in U.S. Pat. No. 5,645,423 and includes double helical loops located on each side of a central segment. In U.S. Pat. No. 5,678,990, one of the linkages comprises a spring-loaded telescoping assembly.
Other orthodontic devices for correcting Class II and Class III malocclusions are described in U.S. Pat. Nos. 3,798,773, 4,462,800 and 4,551,095. The devices described in these references include telescoping tube assemblies that urge the dental arches toward positions of improved alignment. The assemblies are securely coupled to other orthodontic appliances such as brackets or buccal tubes by the practitioner, and the problems of patient non-compliance are avoided.
Another type of telescoping tube assembly for repositioning the dental arches is described in U.S. Pat. No. 5,711,667. In this patent, a spring is provided to urge a plunger in a direction away from a cylinder to achieve desired movements of the patient's teeth. The spring is described in this reference as being located within the cylinder or external of the cylinder in either coaxial relation or offset, parallel relation to the central axis of the plunger.
U.S. Pat. No. 5,562,445 describes another intra-oral device for moving the position of one dental arch relative to the other. The device disclosed in U.S. Pat. No. 5,562,445 includes first and second telescoping cylinders and a plunger received in the first cylinder. A spring in the first cylinder urges the plunger and the first cylinder in directions away from each other, while the first cylinder and the second cylinder are freely slidable relative to each other.
Although a variety of devices including intra-oral telescoping assemblies for correcting Class II and Class III malocclusions have been suggested in the past as noted above, there is a continued need in the art to improve existing options and to provide new devices that represent alternatives for treatment Preferably, such new alternatives would function reliably and efficiently so treatment time is not lengthened, yet also be of simplified construction that would not be prone to breakage or cause difficulties during its manufacture.